As you know, Rosario comes up with rich linking abilities for workitems and object model to support it. Working with object model could be a bit tricky when it comes to comprehending directions of links and Durgaprasad wrote a nice blog on how to use the OM. Check it out here: http://blogs.msdn.com/dgorti/archive/2007/09/26/querying-on-workitem-links-through-the-api.aspx . Note that the actual querying for links based on criteria can be done with WIQL language.